Issue 42, 2011

Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl2 and Au(i) complexes

Abstract

The intramolecular [4C+3C] cycloaddition reaction of allenedienes catalysed by PtCl2 and several Au(I) complexes has been studied by means of DFT calculations. Overall, the reaction mechanism comprises three main steps: (i) the formation of a metal allyl cation intermediate, (ii) a [4C(4π)+3C(2π)] cycloaddition that produces a seven-membered ring and (iii) a 1,2-hydrogen migration process on these intermediates. The reaction proceeds with complete diastereochemical control resulting from a favoured exo-like cycloaddition. Allene substituents have a critical influence in the reaction outcome and mechanism. The experimental observation of [4C+2C] cycloadducts in the reaction of substrates lacking substituents at the allene terminus can be explained through a mechanism involving Pt(IV)-metallacycles. With gold catalysts it is also possible to obtain [4C+2C] cycloaddition products, but only with substrates featuring terminally disubstituted allenes, and employing π-acceptor ligands at gold. However the mechanism for the formation of these adducts is completely different to that proposed with PtCl2, and consists of the formation of a metal allyl cation, subsequent [4C+3C] cycloaddition and a 1,2-alkyl shift (ring contraction). Electronic analysis indicates that the divergent pathways are mainly controlled by the electronic properties of the gold heptacyclic species (L-Au-C2), in particular, the backdonation capacity of the metal center to the unoccupied C2 (pπ-orbital) of the intermediate resulting from the [4C+3C] cycloaddition. The less backdonation, (i.e. using P(OR)3Au+ complexes), the more favoured is the 1,2-alkyl shift.

Graphical abstract: Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl2 and Au(i) complexes

Supplementary files

Article information

Article type
Paper
Submitted
06 Jun 2011
Accepted
12 Aug 2011
First published
06 Sep 2011

Dalton Trans., 2011,40, 11095-11105

Theoretical study on intramolecular allene-diene cycloadditions catalyzed by PtCl2 and Au(I) complexes

S. Montserrat, I. Alonso, F. López, J. L. Mascareñas, A. Lledós and G. Ujaque, Dalton Trans., 2011, 40, 11095 DOI: 10.1039/C1DT11061F

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements